WO1994025763A1

WO1994025763A1 - Thread-forming screw

Info

Publication number: WO1994025763A1
Application number: PCT/EP1994/001382
Authority: WO
Inventors: Stefan Hettich; Ulrich Hettich
Original assignee: Firma Ludwig Hettich Schraubenfabrik Gmbh & Co.
Priority date: 1993-05-04
Filing date: 1994-05-02
Publication date: 1994-11-10
Also published as: JPH08509537A; US5674035A; EP0697071A1; AU676917B2; AU6841894A; DK0697071T3; EP0697071B1; CA2160890C; ATE149645T1; CA2160890A1; ES2100069T3; DE59401955D1; EP0625400A1

Abstract

A thread-forming screw that can be screwed directly into concrete, stone or the like has a screw head (11), a screw shank (12) and a thread (14) which extends at least partly over the length of the screw shank. The invention provides that the ratio of the outside diameter (da) to the core diameter (dk) of the screw is about 1.25 to 1.5, the ratio of the outside diameter (da) to pitch (p) is about 1.5 to 1.6, and the flank angle (α) of the thread (14) is less than 50° and at least 35°.

Description

THREAD-FORMING SCREW

The invention relates to a thread-forming screw with the features of the preamble of claim 1.

A known screw of this type (CH-A-651 115) has a thread with a ratio of the outside diameter to the pitch of approximately 2.5 and a flank angle in the range between 50 ° and 65 °. In one embodiment, a ratio of the outer diameter to the core diameter of approximately 1.3 is realized.

The invention is based on the object of designing a thread-deforming screw of the type specified in the preamble of claim 1 in such a way that simple and reliable fastening of components to concrete or masonry is possible without the use of dowels or other aids.

Claim 1 serves to achieve this object.

In the thread-forming screw according to the invention, the dimensioning parameters GÖS thread are selected such that

little thread is engaged so that the torque in hard material, such as concrete, is not too great;

the distance between two turns of the thread is sufficiently large to take into account the property of the concrete, essentially being able to transmit compressive forces and only small tensile forces. According to a further development of the invention, the screw shank has recesses on either side of the threaded foot for receiving the broken-out concrete or stone powder, which is known per se for a wood screw for another purpose, namely to improve the holding effect.

In claims 3 to 5 further dimensioning regulations are given, which relate the pitch p, the core diameter d _jj and the outer diameter d _{a of} the thread in relation to the diameter d ^ of the bore to be predrilled in the concrete or the masonry. For the above-mentioned sizes, claims 3 to 5 specify ranges within which the screw brings optimum results with regard to the screwing-in torque and the holding effect.

From EP 89 123 699.4 a thread-forming screw is known, in which the thread burr has bow-shaped incisors. The known screw is designed for screwing into wood or chipboard material. Surprisingly, the use of such incisors also results in the screw according to the invention being screwed in much more easily into the brittle, easily breaking concrete, but also into masonry or stone. A configuration according to claim 7 is preferred.

In a modification of the known screw according to EP 89 123 699.4, it is preferred for the screw according to the invention that the recesses forming the cutting teeth have a depth which corresponds to 5/7 to 7/7 of the thread height.

Concrete is a material that tends to crack. To ensure that the screw is sufficiently resilient even in the event of crack formation, for example due to The features of claim 12 are provided in a preferred embodiment of the invention in order to ensure tensile stress under the load of the screw. The claimed small angle of attack, which leads to an asymmetrical shape of the thread cross-section, avoids abrasive wear of the concrete in the crack area due to relative movements between the screw head-side thread flank and the concrete.

The screw according to the invention can also be designed as a tool for forming a threaded hole in concrete, stone, masonry or the like. A screw with a thread according to claim 1 can then be easily screwed into a threaded hole formed with such a tool, such a screw then leaving out incisors according to claim 6 or 7.

Further refinements of the invention are specified in the further subclaims.

The invention is explained in more detail below with the aid of schematic drawings of exemplary embodiments with further details.

Show it:

1 shows a screw according to the invention in a side view;

2 shows a modified screw according to the invention;

Figure 3 is a partial section in the direction of arrows III-III in Fig. 4.

4 shows a partial section in a plane containing the thread burr of a partial area of the thread;

Fig. 5 is a partial view in the direction of the arrow V in Figure 4 in a developed representation.

6 shows a partial section in a plane containing the thread burr of a partial area of the thread of a modified screw according to the invention;

Fig. 7 is a view in the direction of arrow VII in Fig. 6 in a developed representation;

8 shows a partial view of a screw shaft with a thread modified according to the invention, with incisors not shown;

9 shows a partial section in the direction of arrows IX-IX in FIG. 10 through the screw shaft according to FIG. 8 with an asymmetrical thread profile;

10 shows a partial section through the screw shaft according to FIG. 8 in one plane containing the thread burr;

Fig. 11 is a developed partial view in the direction of arrow XI in Fig. 10;

12 shows a partial section in the direction of arrows XII-XII in FIG. 13 through the screw shaft according to FIG. 8 with modified incisors;

13 shows a partial section like FIG. 10 in a plane containing the thread burr;

Fig. 14 is a developed partial view in the direction of arrow XIV in Fig. 13 and

15 shows a screw designed as a tapping tool according to the invention.

The screw shown in FIG. 1 has a screw head 11, a cylindrical screw shaft 12 and a frusto-conical screw tip 13 to facilitate the insertion of the screw into a borehole 10.

A thread 14 extends the length of the sheep tes 12 up to the frustoconical end 13. 15 denotes the thread burr, ie the peripheral outer edge of the turns of the thread 14.

The following mean:

dα. - Outside diameter, measured via the thread burr 15; d _jj - core diameter of the shaft 12; d _j , - hole diameter of the predrilled hole

10; p - pitch between two turns of the screw; - flank angle of the thread.

The dimensions mentioned are related to each other in the following relationships (1), (2) and (3):

0.6; (1)

1 ≥ £ _k ≥ 1 - Q__ L (2) ^d b ^d bd, = -0.0277 d _h ² + 1.491 d _h - 0.447. (3)

These relationships or equations also apply to the modification according to FIG. 2, in which the same parts are designated with the same reference numerals and are not described again.

The only difference in comparison to the embodiment according to FIG. 1 is that recesses 8, 9 are provided on both sides of the thread 14 for receiving the broken-out concrete or stone powder. This makes it even easier to screw the screw into concrete or masonry.

In the embodiment according to FIGS. 3 to 5, the thread burr 15 is spaced at intervals by recesses 16. broken, in such a way that the remaining burr sections form cutting teeth 17 with the cutting edge 17a pointing in the screwing-in direction of the screw. The division for the incisors is made, for example, in such a way that, depending on the diameter, six to thirty teeth are formed per turn. The recesses 16 interrupting the thread burr 15 are designed in such a way that a flat surface 18 forms at the base of the recess, which acts as a lock in the direction of unscrewing the screw. The cutting flanks 19 forming the cutting edge 17a cut the thread flank surfaces 21 at an angle 20 of preferably 75 to 100 degrees, specifically at edges 22.

FIGS. 6 and 7 show a modification which differs from the embodiment just described only with regard to the design of the base of the recesses 16. In the case of the modification, the surface representing the base of the recesses 1.6 is not designed as a flat surface 18 but as a wedge 23, the wedge edge 24 merging into the thread burr 15. The wedge surfaces 25 of the wedge 23 form an angle of preferably 60 to 100 degrees and cut the thread flank surfaces 21 in the edges 27. This has the effect that, when the screw is screwed in, the material loosened by the cutting edges 17a more easily over the inclined surfaces 25 can be dissipated to the thread base.

The depth of the recesses 16 forming the cutting teeth 17 is preferably between 5/7 and 7/7 of the thread height of the thread 14. The cutting edge 17a is expediently at an angle 28 which is negative with respect to the radial direction 28 between 25 ° and 35 ° to the screw radius 30. The surface 18 or the wedge edge 24 preferably has an angle 29 to the tangent 31 of 20 to 32 degrees. All transitions of the surfaces intersecting the thread flank surfaces are to be designed in such a way that there are no sharp edges which Material flow would impair.

The embodiments shown in FIGS. 8 to 11 on the one hand and 12 to 14 on the other hand show modifications of the design of the thread, in both cases the angle of attack β of the thread flank 14 facing away from the screwing direction E or facing the screw head coinciding according to FIG 'with respect to a plane perpendicular to the longitudinal axis of the screw is smaller than the angle of attack of the screw-side thread flank 14 "which is not shown in the figures. This angle of attack ß is preferably between 2 ° and 5 ° the longitudinal axis of the screw relative movements between the thread flank 14 'and the concrete do not lead to an abrasive effect on the concrete and thus the tendency of loosening and possibly pulling out of the screw from its hole in the concrete is counteracted under load.

An asymmetrical thread profile results from the different angular inclination of the two ^' flanks 14', 14 ', as can be clearly seen in FIGS. 9 and 12.

Furthermore, there are modifications of the incisors, the design according to FIGS. 9 to 11 principally corresponding to that according to FIGS. 6 and 7 and the design according to FIGS. 12 to 14 principally corresponding to that according to FIGS. 3 to 5. For this reason, the designs of the incisors are no longer described in detail, but reference is made to the corresponding designs according to FIGS. 3 to 7, the simplicity of both designs according to FIGS. 9 to 11 on the one hand and 12 to 14 on the other hand the same reference numerals are used as in FIGS. 3 to 7. It should only be pointed out that the flank angle α is 40 ° in both versions and that the angle γ in the version according to FIGS. 9 to 11 is 84 ° and in the version according to FIGS. 12 to 14 65 ° wearing. These values lie in the range from 60 to 100 ° given above in connection with FIGS. 6 and .7. The angles 28 and 29 in the embodiments according to FIGS. 8 to 14 are also within the ranges as indicated above for FIGS. 3 to 7. Specifically, the angle 28 here has a value of 34 ° and the angle 29 has a value of 31 °.

Finally, the angle 20 has a value of 98 ° in the embodiment according to FIGS. 9 to 11 and a value of 78 ° in the embodiment according to FIGS. 12 to 14, which means that this angle 20 in the above for the embodiment 3 to 7 specified range from 75 to 100 °.

The screw shown in FIG. 15 is designed as a thread drilling tool for producing a threaded hole in concrete, masonry or the like. The tool has a clamping part 1 with four or more edges, with which the tool can be clamped into a drilling device, an adjoining smooth shaft part 2 of circular cross-section, an adjoining threaded part 4 and a thread cutting part 5, which is weakly conical with a cone angle δ between 1.5 and 3 °, preferably about 2 °, and on which the thread 4 continues up to the end face 6 of the tool.

In the tool shown, the length 1 of the threaded part 5 to the length k of the guide part 3 is about 4: 5. This results from the small preferred cone angle δ = 2 ° of the thread cutting part 5. It is important that the thread 4 on the bore 7 in the The concrete-facing surface 6 of the tool is attached so that the thread cutting process can begin immediately when the tool is sunk into the bore 7.

For the sake of simplicity, FIG. 15 does not show the incisors explained on the basis of FIGS. 3 to 14, which can be distributed around the thread burr as in the other embodiments.

Tapping tools are usually made of metal. The insertion of the incisors into the thread burr can be difficult. Therefore, as an alternative to the cutting teeth described so far, cutting teeth produced by axially parallel profile grooves can be provided, which extend approximately over the thread height h of the thread 4. Such incisors can also be provided together with the incisors explained above with reference to FIGS. 3 to 14.

When the tool is screwed into a hole 7 drilled in the concrete, the wedge-shaped teeth of the thread 4 are pressed into the concrete with high pressure. The wedge action of the teeth results in local overstressing in the concrete, which results in the formation of broken scraps and ultimately the splintering of the concrete. By means of this separating mechanism, the desired internal thread is finally formed in the concrete.

A screw provided with a thread according to FIGS. 1 to 14 can then be screwed directly into the internal thread produced in this way, which screw also provides good holding of parts to be held on the concrete or masonry without the use of a dowel. However, such a screw does not require any incisors, as are described with reference number 16 with reference to FIGS. 3 to 14.

Claims

PATENT CLAIMS

1. Thread-forming screw for direct screwing into concrete, masonry or the like, the thread (14; 4) of which extends at least partially over the length of the screw shank, characterized in that the ratio of the outside diameter (d _a ) to the core diameter ( d _κ ) of the screw is approximately 1.25 - 1.5, that the ratio of the outer diameter (d _a ) to the pitch (p) of the thread (1; 4) is approximately 1.5 - 1.6 and that the flank angle ( α) of the thread (14; 4) is less than 50 ° and greater than or equal to 35 °.

2. Screw according to claim 1, characterized in that the screw shank has recesses (8, 9) on both sides of the threaded foot for receiving broken-out rock powder.

3. Screw according to claim 1 or 2, characterized ge ¬ indicates that the slope (p) with respect to the bore diameter (d _j -.) Of a pre-drilled hole for receiving the screw (10) behaves as follows:

0.6 ^d b

4. Screw according to one of claims 1 to 3, characterized in that the Kern¬ diameter (d _jj ) with respect to the bores diameter (d _b ) behaves as follows:

1 ≥ ä-. ≥ 1 - 0.5 ^d b ^d b

5. Screw according to one of claims 1 to 4, characterized in that the outer diameter (d _a ) with respect to the bore diameter (d _j .,) As. behaves as follows:

d _a = -0.0277 d _b ² + 1.491 d _b - 0.447

6. Screw according to one of claims 1 to 5, characterized g e k e n n z e i c h n e t that the thread burr

(15) of the thread (14; 4) has bow-shaped incisors (17).

7. Screw according to claim 6, characterized in that the thread burr (15) of the thread (14) is interrupted at intervals by recesses (16), that between the recesses

(16) standing burr sections form the bow-shaped incisors (17) and that the cutting edges (17a) of the incisors (17) point essentially in the screwing-in direction of the thread (14) and at a negative angle (28) the radial direction (30) are employed.

8. Screw according to claim 6 or 7, characterized ¬ indicates that six to thirty incisors (17) are provided per turn of the thread (14; 4).

9. Screw according to one of claims 6 to 9, characterized in that the recesses (16) forming the cutting teeth (17) have a depth (t) which corresponds to 5/7 to 7/7 of the thread height (h).

10. Screw according to one of claims 7 to 9, characterized in that the negative angle (28) of the cutting edges (17a) of the cutting teeth (17) is 25 ° to 35 °.

11. Screw according to one of claims 1 to 10, characterized in that an extension, in particular a screw bolt with a metric thread, is provided instead of or in the extension of the screw head (11).

12. Screw according to one of claims 1 to 11, characterized in that the setting angle (β) of the thread flank (14 ') facing away from the screwing direction (E) is smaller than the setting angle of the screw-side thread flank with respect to a plane perpendicular to the longitudinal axis of the screw (14 '') and is preferably between 2 ° and 5 °.

13. Screw according to one of claims 1 to 12, characterized in that it is used as a tool for producing an internal thread in concrete, stone or the like with a clamping part (1), a shaft part (2) and a thread part (4) having a guide part (3) constant diameter and a weakly tapered threaded part (5).